#include<stdio.h>
int main()
{
	double a = 2.0, b = 1.0;
	int n;
	int i;
	scanf("%d", &n);
	double sum=0.0;
	for (i = 1; i <= n; i++)
	{int x;
		sum=1.0* a / b +sum;
		x=a;
		a+=b;
		b=x;


	}
	printf("%.2f", sum);

	return 0;
}
